1. Field of the Invention
The invention relates to a process for the purification of crude nitrobenzaldehyde containing undesired positional isomers by treatment with water in the presence of an emulsifier.
2. Description of the Related Art
It is known from Houben-Weyl, Methoden der organischen Chemie (Methods of Organic Chemistry), Volume X/1, page 600 (1971) that a mixture of three possible isomers results from the nitration of benzaldehyde.
For the purification of the desired nitrobenzaldehyde, a recrystallization from organic solvents can be undertaken. By this means, serious losses of the desired product and considerable solvent costs results. When working on a commercial scale, additional precautions are necessary with regard to operational safety, recovery of the solvent, and health and environmental protection.
The recrystallization of organic materials from water in the presence of detergents is discussed in J. Org. Chem. 21 (1956), pp. 1445-1447. It was observed that the crystallization rate in the presence of surface-active agents is strongly lowered with organic compounds having limited water solubility. The procedure necessary is troublesome and characterized in that the organic substance only goes into solution slowly even on heating to boiling point, and in that a complete solution must be present, however, which is achieved, if appropriate, by hot filtration of undissolved constituents. Should the crystallization begin in the hot filtrate, it is heated once more to complete dissolution and slowly cooled. Data concerning the type and amount of the original impurities and data about the degree of purity obtained are not given.